ELEPHANT AND MASTODON. 35 



North American Mastodon, being only distinguishable in a thin 

 layer under the microscope. It is more abundant upon the fangs. 

 The anterior ridge is supported by two stout united fangs, and the 

 three posterior ridges by fangs agreeing with them in number, 

 but more or less confluent into an irregular hollow cone. 



In the existing Indian Elephant, the last grinder of the upper 

 jaw is of a subtriangular rhomboidal form in the vertical section, 

 widely different from that of the North American Mastodon. The 

 crown is very high in front, and declines rapidly behind. In a 

 large specimen of this tooth from Assam, the dimensions are 

 upwards of fourteen inches of length, by eight inches of height in 

 front, which is reduced to about one-third at the last ridge, while the 

 width does not exceed three inches at the anterior end, from which 

 it narrows gradually behind. The coronal surface is convex 

 across, and also in the antero-posterior direction. There is no 

 indication of the longitudinal cleft, which, in the North American 

 and other Mastodons, bisects the crowns of the molars into lateral 

 segments. The ridges, which in the first-mentioned species do 

 not exceed four, are multiplied in the last upper grinder of the 

 Indian Elephant to twenty-three or twenty-four thin plates, which 

 terminate upwards in slender, cylindrical digitations, hence called 

 Cheirolites, by the early palaeontologists, when found separate. 

 The cement substance enters largely into the composition of the 

 tooth, being interstratified with the enamel plates in a layer which 

 also envelopes the entire body of the tooth. The fangs are slender, 

 and numerous, bearing a relation to the lamellae but they are con- 

 fluent into large hollow groups, which are of inconsiderable length, 

 as the tooth is held firm in the jaw by a large portion of the crown 

 being imbedded in the alveolus. Instead of being protruded in a 

 nearly horizontal direction, as in the North American Mastodon, 

 the teeth move forwards in the arc of a circle ; the anterior plates 

 in the upper grinders are inclined forwards, and by the process of 

 wear they are ground down, so that the front part of the tooth is 

 truncated obliquely (pi. 1, fig. 2, and pi. ?, fig. 4.) long before 

 the posterior lamellae come into use. The plane of detrition makes 



d 2 



